“Implants that dissolve in the body after they’ve done their work could solve biocompatibility problem”

Researchers at the University of Illinois at Urbana-Champaign and Tufts University say they have invented functional electronic implants that can dissolve after programmable time periods. To demonstrate the system, which could aid in healing during the first few crucial days after an operation, they implanted one in a rat. It created a temporary temperature increase to sterilize a wound, and then it dissolved after 15 days. The researchers reported the development this week in the journal Science.

Biomedical researchers are turning to the idea of “programmable degradation” because it is difficult to develop materials that remain compatible with human tissue over the long term. Medical implants or drug-delivery systems that do their work and then disappear are ideal. To develop the electronic implants, the researchers encased them in silk. That material’s characteristics, particularly its crystallinity, can be adjusted so that its degradation time can be anywhere from seconds to years.

The electronics inside the silk were based on nanometers-thick sheets or ribbons of silicon, called silicon nanomembranes. The materials have been previously used to make experimental transistors, diodes, complementary logic devices, and photocells for flexible surfaces. Whereas a conventional silicon wafer or a chip would take about a thousand years to dissolve in biofluids, says John A. Rogers, who led the research at the University of Illinois, a nanomembrane is gone in a couple of weeks.

Working with the team at Illinois, Tufts researchers provided expertise on silk and carried out the animal experiments. Analytical modeling was done at Northwestern University in collaboration with Dalian University of Technology, in China, and a University of Arizona clinician identified the heat-therapy application.

While there have been no human trials yet, the component materials of the system are found in implants that have been approved by government regulators for other medical uses, Rogers points out. Silk is approved for sutures, magnesium is used for intravascular stents, and silicon is used for drug-delivery systems. “You have to do trials, because biology is complicated,” Rogers says, “but the materials are not complicated.”

The researchers tested a host of such transient components like inductors, capacitors, resistors, diodes, and transistors. All the components disintegrated and dissolved when immersed in deionized water. The materials and fabrication techniques may be used to make components for electronic systems in complementary metal-oxide semiconductor (CMOS) logic.

“Here is this toolbox that you can make anything with,” says Christopher J. Bettinger, a biomaterials researcher at Carnegie Mellon University who was not involved in the research, adding that the work was a remarkable feat of integration that neatly combined pieces from several areas. It’s also a very flexible system, he says; for example, the silk substrate could be swapped with other biodegradable polymers.

Jeffrey Borenstein, a researcher at the Charles Stark Draper Laboratory in Massachusetts, was also impressed. “As a general demonstration, this is very powerful,” he says. “When it comes to specific applications, you will have to evaluate how each of these materials performs inside the body.”

One challenge ahead could be finding additional ways to power the implants. The first version was powered by RF energy, but RF coils “are just very sensitive to orientation,” Bettinger says, adding that if you have a patient who moves around, it might change the power requirements.

The Illinois researchers, however, might have something in their favor. There is a synergy, Rogers says, between their work and the multibillion-dollar semiconductor industry that isn’t immediately obvious. As with conventional CMOS devices, with transient electronics, thinner is better. “I think we will be able to bootstrap off of advances in conventional electronics,” he says.

Today’s the kind of day when you can see the future. Today, the U.S. Food and Drug Administration (FDA) approved the first treatment that can restore (limited) eyesight to (some) blind people. Despite the caveats, it’s an exciting milestone.

The treatment involves electrodes implanted in the eyes of people whose retinas are damaged. The FDA approved the implants for people with severe cases of retinitis pigmentosa, a relatively small patient population. But the company that makes the implants, Second Sight Medical Products, says they can benefit a much broader group of people with vision problems, including many elderly people who suffer from macular degeneration.

IEEE Spectrum covered the technology in “Birth of the Bionic Eye.” One of the test subject, Barbara Campbell (pictured).

That article was part of the “Top Tech 2012” special report based on Second Sight’s optimistic predictions that it would win FDA approval for the implants in the year 2012. So the company is a couple of months behind schedule in the United States, but its implants have been on the market in Europe since 2011.

Second Sight isn’t the only company working on retinal prostheses.They have also described a competing technology from the German company Retina Implant AG, whose system was undergoing clinical trials last year.

What if you could plant a listening device in a single cancer cell, a bug that would follow the cell’s movements, eavesdrop on its metabolism and tell you what it’s up to?

A group of Stanford University researchers has made a start with a minuscule optical-cavity splinter small enough to insert in single cells and light enough remain embedded as the cells move about and multiply.

Gary Shambat and colleagues in Jelena Vuckovic’s Nanoscale and Quantum Photonics Lab built up a gallium arsenide wafer studded with three layers of indium arsenide quantum dots. They then etched away the supporting substrate, leaving a tapering, 200-micrometer-long beam tipped with a blade 20 micrometers long, 400 to 650 nanometers wide, and 220 nanometers thick. The business end of the blade looks like a strut from an infinitesimal Meccano Erector set: it’s pierced by 20 holes (averaging 120 nm across, though their diameters and spacing diminish towards the tip); five of the holes constitute an optical cavity, a hall of mirrors that resonates at a wavelength close to the quantum dots’ 1350 nm photoluminescence.

Like so many ultra-small optical devices, the nanocavity probe’s resonant frequency changes when molecules from its environment adhere to the beam’s surface. In this case, the emitted light shifts about 6 nm to the red for every 10 nm of film thickness. In a properly constructed assay, the thickness of the film will be a function of the specific substances sticking to the probe.

Shambat, Vuckovic, and their collaborators demonstrated this phenomenon by accurately detecting the binding of streptavidin (a protein produced by Streptomyces) to biotin (vitamin B7). (The binding between the two molecules is extraordinarily strong, and serves as the foundation of countless bioassays.) The researchers coated the nanoprobe with biotin. They found that random binding of streptavidin to the probe prompted a 0.5 nm red shift, while the stronger biotin-streptavidin binding produced shifted the luminescence peak by 3.5 nm.

When further developed, the device could offer an additional tool in the increasingly important study of single living cells. “Let’s say you have a study that is interested in whether a certain drug produces or inhibits a specific protein. Our biosensor would tell definitively if the drug was working, and how well, based on the color of the light from the probe. It would be a powerful tool,” said co-author Sanjiv Sam Gambhir, chair of the Stanford Medical School radiology department.